THE PERIODIC TABLEDOE-HDBK-1015/1-93Fundamentals of ChemistryCH-01Rev. 0Page 20The electron shells represent major energy states of electrons. Each shell contains one or moresubshells called orbitals, each with a slightly different energy. In order of increasing energy, theorbitals are designated by the small letters s, p, d, f, g, h.No two shells consist of the same number of orbitals. The first shell contains only one orbital,an s orbital. The second shell contains s and p orbitals. In general, each higher shell containsa new type of orbital:the first shell contains an s orbital,the second shell contains s and p orbitals,the third shell contains s, p, and d orbitals,the fourth shell contains s, p, d, and f orbitals,and so on. Each orbital can hold a definite maximum number of electrons. There is also a limitto the number of electrons in each shell and the limit increases as one goes to higher shells. Thenumbers of electrons that can occupy the different orbitals and shells are shown in Table 4.TABLE 4Electrons,Orbital, and Shell Relationships in Atomic StructureShell NumberType of OrbitalsMaximum Number of ElectronsMaximum Totalin Each OrbitalElectrons in shell1s2228s2p6318p6s2d10432s2p6d10f14550d10s2p6f14g18